Background: Bacteria of the genus Asaia have been recently recognized as secondary symbionts of different
sugar-feeding insects, including the leafhopper Scaphoideus titanus, vector of Flavescence dorée phytoplasmas.
Asaia has been shown to be localized in S. titanus gut, salivary glands and gonoducts and to be maternally
transmitted to the progeny by an egg smearing mechanism. It is currently not known whether Asaia in S. titanus is
transmitted by additional routes. We performed a study to evaluate if Asaia infection is capable of horizontal
transmission via co-feeding and venereal routes.
Results: A Gfp-tagged strain of Asaia was provided to S. titanus individuals to trace the transmission pathways of
the symbiotic bacterium. Co-feeding trials showed a regular transfer of bacterial cells from donors to recipients,
with a peak of frequency after 72 hours of exposure, and with concentrations of the administrated strain growing
over time. Venereal transmission experiments were first carried out using infected males paired with uninfected
females. In this case, female individuals acquired Gfp-labelled Asaia, with highest infection rates 72-96 hours after
mating and with increasing abundance of the tagged symbiont over time. When crosses between infected females
and uninfected males were conducted, the occurrence of “female to male” transmission was observed, even
though the transfer occurred unevenly.
Conclusions: The data presented demonstrate that the acetic acid bacterial symbiont Asaia is horizontally
transmitted among S. titanus individuals both by co-feeding and venereal transmission, providing one of the few
direct demonstrations of such a symbiotic transfer in Hemiptera. This study contributes to the understanding of
the bacterial ecology in the insect host, and indicates that Asaia evolved multiple pathways for the colonization of
S. titanus body.

Background: Bacteria of the genus Asaia have been recently recognized as secondary symbionts of different
sugar-feeding insects, including the leafhopper Scaphoideus titanus, vector of Flavescence dorée phytoplasmas.
Asaia has been shown to be localized in S. titanus gut, salivary glands and gonoducts and to be maternally
transmitted to the progeny by an egg smearing mechanism. It is currently not known whether Asaia in S. titanus is
transmitted by additional routes. We performed a study to evaluate if Asaia infection is capable of horizontal
transmission via co-feeding and venereal routes.
Results: A Gfp-tagged strain of Asaia was provided to S. titanus individuals to trace the transmission pathways of
the symbiotic bacterium. Co-feeding trials showed a regular transfer of bacterial cells from donors to recipients,
with a peak of frequency after 72 hours of exposure, and with concentrations of the administrated strain growing
over time. Venereal transmission experiments were first carried out using infected males paired with uninfected
females. In this case, female individuals acquired Gfp-labelled Asaia, with highest infection rates 72-96 hours after
mating and with increasing abundance of the tagged symbiont over time. When crosses between infected females
and uninfected males were conducted, the occurrence of “female to male” transmission was observed, even
though the transfer occurred unevenly.
Conclusions: The data presented demonstrate that the acetic acid bacterial symbiont Asaia is horizontally
transmitted among S. titanus individuals both by co-feeding and venereal transmission, providing one of the few
direct demonstrations of such a symbiotic transfer in Hemiptera. This study contributes to the understanding of
the bacterial ecology in the insect host, and indicates that Asaia evolved multiple pathways for the colonization of
S. titanus body.